| A | B |
|---|
| eras | major subdivision of geological time based on differences in life-forms |
| trilobites | organisms that lived hundreds of millions of years ago with bodies divided into three sections |
| Precambrian | the longest geological part of Earth's history |
| cyanobacteria | one of the earliest life-forms, which gave off oxygen |
| birds | flying animals that evolved from dinosaurs |
| Pangaea | the single landmass that once contained all Earth's continents |
| epoch | smaller units of time in a geologic period |
| Jurassic | the time period where dinosaurs were the dominate life-form |
| geologic time scale | the division of Earth's history into time units |
| eons | the longest subdivisions of geologic time |
| periods | major divisions of an era |
| organic evolution | the change in organisms over time. |
| species | a group of organisms that normally reproduce with other members of their group |
| natural selection | process by which certain organisms survive and reproduce |
